Prior to the actual starting of a power loom, that is prior to an electrical signal that activates the above mentioned clutch, the flywheel mass is driven by the main drive motor of the loom until an increased start-up or run-up r.p.m. relative to a rated operational r.p.m. of the loom has been reached. With or just prior to the engagement or activation of the clutch, which connects the flywheel mass to the main drive shaft of the loom, the electric drive motor is disconnected from the flywheel mass during a starting transition phase. Preferably, the same signal that engages the clutch temporarily disconnects the electric drive motor. Thereafter, the normal power supply to the electric drive motor is switched on with a certain time delay that depends on the reduction of the instantaneous r.p.m. of the flywheel masses substantially to the rated operational r.p.m. The switch-on of the drive motor takes place when the r.p.m. of the flywheel masses approaches the rated operational r.p.m. of the power loom.
U.S. Pat. No. 4,837,485 (Meroth et al.) the disclosure of which is incorporated herein by reference, describes a method and system for starting a power loom, wherein the above described operation is employed. The above mentioned time delay is adjustable. However, there is room for further improvement, especially in connection with modern high performance power looms for avoiding weaving faults, especially start-up faults.
During the operation of high performance power looms it can occur that, due to the high operational or rated r.p.m., the fabric appearance changes as a function of time, especially with regard to starting sections, creeping sections, and loom stop sections within the fabric. In practice, this fact may lead to faults in the fabric, and these faults may differ from one type of fabric to another. Such faults may occur, for example, in a loom in which the shut-down time of the electrical motor drive during flywheel start-up is adjusted to two minutes, while the actual shut-down time becomes shorter or longer. These faults are known as start-up faults.
The just described faults in the fabric are caused by the fact that new thread spinning methods result in new types of threads or yarns which have a smaller elasticity compared to older types of yarns. Such new types of yarns are, for example, open-end yarns, acetate yarns, and viscose or cellulose yarns. An open-end yarn is spun of chopped fibers providing a yarn with a desirable optical appearance, but which is very sensitive to mechanical stress. The reduced elasticity of such yarns causes creeping which, in this context, means a permanent deformation of the yarn when its elasticity limit is exceeded by the stretching of the yarn during the weaving. Such deformations cause fabric faults and the newer types of yarns cause such faults quite frequently. As a result, any down times of the loom caused by these modern yarns require evermore attention. Taking these faults into account and also considering the abilitie of individual operators, down times of up to 30 minutes are considered to be realistic in present loom operations including high performance looms. These down times should be reduced.
In the just described prior art, the flywheel of the loom is accelerated during a predetermined down time and the flywheel in turn accelerates the main loom drive shaft to an r.p.m. above the operational r.p.m. Such an operation has the disadvantage that the fixed run-up time frequently is insufficient for accelerating the main drive shaft to a required higher r.p.m. than the rated r.p.m. Incidentally, the higher r.p.m. is also referred to as the desired or selectable r.p.m. The time needed by the loom for reaching the higher selectable r.p.m. depends on a plurality of factors, for example, the temperature of the lubricant, the warp thread tension, the type of binding, the number of shafts or heald frames, the operating temperature of the entire loom, and other parameters. These parameters change with time. Therefore, it is not always possible to reach the required selectable r.p.m. during the fixed time period available for this purpose heretofore.